In the field of electromechanical switchgear, prior industry practice requires that some form of blocking device be incorporated in a switchgear's operating system to prevent the switchgear operator from inadvertently connecting an energized feeder line to a ground.
Typically, such switchgear has a plurality of pivotal blades which are connected to an incoming energized feeder line. The blades are pivoted between three positions, two of which connect the blades and consequently the feeder line to conductive terminals and one in which the circuit remains open. The switchgear can be utilized in reverse fashion to selectively connect two feeder lines to an outgoing circuit wherein the outgoing circuit is connected to the pivoting blades. Depending on how the switchgear is utilized, it may be necessary to restrict the movement of the blades from contact with one or the other conductive terminals. For instance, if the switchgear is used in a public utility's electric service circuit, the inadvertent switching of the blades and consequently the energized feeder line to a ground terminal could open other protective devices in the circuit thereby turning off power to users.
Blocking devices are commonly used to insure that the switchgear not be thrown to an undesirable position. These devices include blocking cams operatively connected to the switchgear which are locked in place by padlocks once the blades are pivoted to a chosen operating position. The problem with these blocking devices is that should the switch operator forget to connect the padlock or connect the padlock incorrectly, the blocking device is rendered useless in preventing inadvertent switching of the blades to an undesirable position. Should the operator need to quickly switch the blades to an open position, the use of padlocks could hinder such action as padlocks require a substantial time period for disengagement and a correct set of keys.